Glucose is an important source of energy to the cells in the human body and is abundantly present in food ingredients. After consumption of starch or other dietetic available sources of glucose and their subsequent digestion, glucose is released in the gastro-intestinal tract, where it is rapidly and effectively absorbed from the intestinal lumen. This will usually increase glucose concentrations in blood. The change in glucose after consumption of a food is called the postprandial glucose response (PPGR), which can be measured as the area under the curve (AUC), which plots the plasma glucose concentration with time. The human body strives to maintain homeostasis of glucose levels in tissue and blood with time, in order to allow proper functioning of all cells. One important instrument to achieve glucose homeostasis is the release of insulin by the pancreas when the concentration of specific food components like glucose starts to increase. Under normal circumstances this will increase glucose transport into the cell and formation of glycogen using glucose, and trigger other metabolic changes, therewith rapidly causing the blood glucose levels to decrease to normal levels.
A person that does not react properly on released insulin is said to be insulin-resistant. Large groups of persons suffer from insulin resistance like many obese persons, persons suffering from the so-called metabolic syndrome (or syndrome X), diabetics and many patients in hospitals or nursing homes who developed a temporary or longer lasting insulin resistance as a cause of their disease. Part of the diabetics also experience an insufficient capacity to increase insulin concentrations in blood after consumption of food (i.e. post-prandially). Persons that suffer from insulin-resistance demonstrate abnormal high postprandial glucose response, even after consumption of moderate amounts of food ingredients that comprise glucose. When high postprandial glucose concentrations occur relatively frequently and over longer periods of time, they can cause several severe health problems. Known secondary side effects, as can be found in diabetics, are problems in the cardio-vascular system, such as hypertension, atherosclerosis, poor blood supply to peripheral tissues, stroke, heart attacks etc., as well as problems in the kidney, in particular an abnormal glomerular filtration rate, and a wide range of neuropathies and retinopathies like cataract. It was also found that mortality of severe disease in hospital patients is associated with the severity of insulin resistance.
The decrease of postprandial glucose response (PPGR) has been the subject of numerous research efforts. Many types of carbohydrates have been proposed to induce a low PPGR. Also inclusion of dietetic fibre in parental a nutritional product has been proposed for this purpose, for example viscous fibres, like gums or pectin. The disadvantage of using such fibres is the increase in viscosity, leading to bloating, flatulence, loss of appetite and possibly constipation, when used in liquid products in amounts that are effective.
U.S. Pat. No. 6,890,571 teaches the use of slowly digestible starch as a carbohydrate which provides glucose over an extended period of time, e.g. for the treatment of hyperglycemia, insulin resistance, hyperinsulinemia, dyslipidemia, dysfibrinolysis and obesity. The starch according to U.S. Pat. No. 6,890,571 is enzymatically debranched for at least 90% and comprises linear alpha-glucans, preferably a highly crystalline amylose having 5-65 anhydro-glucose units linked by alpha-1,4-D-glucoside bonds and a DE>6.0. No change in the material properties is observed during typical food processing conditions, when included in an amount of 1-50 wt. % in a wide range of food products. During the test, between 22 and 50 wt. % is digested in the first twenty minutes, and 48-74 wt. % is digested within two hours, after start of the test. Table 2 of U.S. Pat. No. 6,890,571 demonstrates the digestibility profile obtained after heating at 85° C. for 20 minutes and cooling and crystallising at room temperature: about 31-40 wt. % is digested during the first 20 minutes (rapidly digestible) and 29-36 wt. % between 20 and 120 minutes (slowly digestible) after start of the test. The document is silent about the behaviour of the ingredient, when it is subjected to heating at higher temperatures and in particular ultra high heat treatments, as can be beneficially used during manufacture of enteral clinical nutrition. It is also silent about the effect of heating in a matrix that comprises proteins and/or lipids and/or other carbohydrate fractions. These components are known to be able to interact with amylose crystallisation and therewith digestibility.
EP-A 0688872 describes a method for producing resistant starch by enzymatic debranching of maltodextrins and retrogradation. The product is commercially available as Actistar RM (resistant maltodextrin).
EP-A 0846704 (U.S. Pat. No. 6,043,229) discloses a retrograded starch having more than 55 wt. % resistant starch, derived from potato or preferably tapioca maltodextrin by dissolution, acidification, debranching by isoamylase treatment followed by spray drying. This resistant starch has more than 50% of linear chains of alpha-glucans having a DP between 10-35 and a DSC melting peak temperature below 115° C. It is suitable for use as a prebiotic component, in particular as a butyrate-producing fibre.
WO05/000904 discloses resistant starch compositions obtained by heating malto-dextrin-derived resistant starch in oil at about 150° C. followed by rapid cooling to about 70° C. and aseptic packaging. For producing a complete food, other components, especially water-based such as proteins and carbohydrates, are separately sterilised and then added to the heat-treated starch-in oil, because otherwise about half of the resistant starch content is lost.
US 2006/0025381 describes a chemically modified starch for controlling providing glucose release over extended periods of time. The resulting modified starch provides less than 25 wt. % glucose at 20 minutes and between 30 and 70 wt. % at 120 minutes. The modification can be achieved by hydroxyalkylation, acetylation, octenyl-succenylation, phosphorylation and the like.
WO 2004/069877 discloses a process of producing a gellable starch product by heating starch having a low amylose content (below 50 wt. %, in particular 20-30 wt. %) to at least 170° C., in particular around 200° C. under mildly acidic conditions, followed by rapid cooling. This document is silent about stability of the slowly digestible starch content.
It was found by the inventors that a commercial resistant starch having a useful content of slowly digestible starch, when stored for some weeks, looses its slowly digestible starch content and turns into a sandy, unattractive product. The disadvantage is especially serious in liquid products, in which the starch forms an undesired sediment after some time.
Hence, it is an object of the invention to provide a process for providing a slowly digestible starch without chemical modification, which is stable under conventional storage conditions.
Another object of the invention is to provide a process for producing a nutritional product, that is effective in rapidly providing glucose to the consumer and maintaining a clinically significant supply of glucose during a prolonged time without resulting in undesirably high concentrations of glucose in the blood, even in persons that have become insulin-resistant.
It is a further object of the invention to a provide nutritional product for persons that suffer from insulin resistance, in order to prevent development of disorders which result from prolonged and frequent high levels of glucose in blood, such as those diseases that result from advanced glycation end-products (AGE), neuropathies, retina problems, and kidney problems.